An organic electroluminescence device (hereinafter, electroluminescence may sometimes be abbreviated as EL) is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang et al. of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Page 913, 1987, or the like), many studies have been conducted on organic EL devices using organic materials as the constituent materials. Tang et al. used tris(8-quinolinolato)aluminum for a light emitting layer and a triphenyldiamine derivative for a hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming exciton which are formed by blocking and recombining electrons injected from the cathode can be increased, and that exciton formed within the light emitting layer can be enclosed. As described above, for the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron-transporting light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer, and an electron-transporting (injecting) layer are well known. In order to increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
Further, as the light emitting material, chelate complexes such as tris(8-quinolinolato)aluminum complexes, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, and oxadiazole derivatives are known. It is reported that light in the visible region ranging from blue light to red light can be obtained by using those light emitting materials, and development of a device exhibiting color images is expected (for example, Patent Documents 1 to 3).
In recent years, a large number of investigations have been conducted on the use of a phosphorescent compound as a light emitting material and the use of energy in a triplet state in EL light emission. A group of Princeton University has reported that an organic light emitting device using an iridium complex as a light emitting material shows high luminous efficiency (Non-patent Document 1). In addition to the organic electroluminescence device using a low molecular weight material as described above, an organic electroluminescence device using a conjugated polymer has been reported by a group of Cambridge University (Non-patent Document 2). In this report, light emission has been confirmed from a monolayer of polyphenylene vinylene (PPV) formed in a coating system.
Recent advances in organic electroluminescence device are remarkable, and characteristics of the organic electroluminescence device allow formation of a thin and lightweight light-emitting device with high luminance under application of a low voltage, wide range of emission wavelengths, and high-speed response, thereby suggesting the possibility of extensive uses.
In association with the significant progress of an organic light emitting device, performance requested of a light emitting material has been growing, and Patent Documents 4 and 5 each disclose a pyrene compound using fluorene as a linker. In addition, Patent Document 6 discloses a pyrene compound using a phenylene or biphenylene group as a linker, and Patent Document 7 discloses tripyrenylbenzene as a comparative example. However, each of the compounds has problems such as an insufficient half life and a poor color purity. Accordingly, a light emitting material from which an optical output with additionally high luminance or additionally high conversion efficiency can be obtained has been requested. In addition, a light emitting material which: takes durability against, for example, a change over time due to long-term use and deterioration due to, for example, an atmospheric gas containing oxygen or moisture, and application to a full-color display or the like into consideration; and emits blue, green, or red light with a high color purity, has been desired.
Patent Document 1: JP 08-239655 A
Patent Document 2: JP 07-183561 A
Patent Document 3: JP 03-200289 A
Patent Document 4: JP 2004-83481 A
Patent Document 5: JP 2004-43349 A
Patent Document 6: JP 2004-139957 A
Patent Document 7: JP 2003-347056 A
Non-patent Document 1: Nature, 395, 151 (1998)
Non-patent Document 2: Nature, 347, 539 (1990)